[baq]

CPUs get microcode updates all the time, too. Nothing is safe from bitrot unless you’re dedicated to 100% reproducible builds and build on the exact same box you’re running on. (…I’m not, for the record - but the more, the merrier.)

[lmm]

> CPUs get microcode updates all the time, too.

To fix bugs, sure. They don't generally get updates that contain new optimizations that radically break existing machine code, justifying this by saying that the existing code violated some spec.

[carlmr]

>To fix bugs, sure.

Maybe your program worked due to the bug they fixed.

[lmm]

Extremely unlikely. CPU bugs generally halt the CPU or fail to write the result or something like that. The Pentium FDIV bug where it would give a plausible but wrong result was a once in a lifetime thing.

[baq]

Spectre and Meltdown exploits stopped working, too. Some of them on some CPUs, anyway.

[lmm]

Sure. But those were obviously exploits from the start. You wouldn't write code like that accidentally.

[ryao]

Do a web search for rdrand and systemd.

[lmm]

> Do a web search for rdrand and systemd.

RDRAND always returning all-FF is exactly the kind of thing that's an obvious bug, not a plausible-but-wrong result.

[ryao]

The other guy said "Maybe your program worked due to the bug they fixed.". The RDRAND fix achieved exactly that.